Pore Hierarchy and Solvent-Dependent Interfacial Dynamics in Three-Dimensional Reduced Graphene Oxide Probed by Low-Field NMR Relaxometry

Porous three-dimensional reduced graphene oxide (3DrGO) combines a hierarchical pore network with tunable surface chemistry, making it an attractive material for applications involving mass transport and interfacial phenomena. In this work, the pore structure and surface properties of 3DrGO were investigated using conventional and low-field nuclear magnetic resonance (NMR) techniques. Scanning electron microscopy (SEM), N2 adsorption–desorption isotherms, X-ray photoelectron spectroscopy (XPS), Carr-Purcell-Meiboom-Gill (CPMG) NMR relaxometry, and Fast Field Cycling (FFC) NMR relaxometry were employed to characterize the material over multiple length scales and probe confined liquid dynamics. While SEM and gas adsorption resolved the macro- and mesoporous structure, CPMG relaxometry revealed several confined liquid populations. Comparison of the NMR relaxation and XPS data suggested that the abundance of oxygen-containing surface groups contributes to differences between polar and nonpolar molecule-surface interactions, with stronger apparent interactions for polar liquids. The desorption behavior was consistent with nonuniform liquid coverage under partially saturated conditions. Analysis of NMR dispersion profiles further indicated a rough, chemically heterogeneous surface, highlighting the potential of low-field NMR techniques as powerful tools for correlating pore architecture, surface chemistry, and molecular dynamics in porous 3DrGO.